Zeolite has pores in the crystal structure of silicon oxide so that many applications utilizing the crystal structure or pores have been reported. In particular, siliceous zeolite substantially free of a metal such as aluminum is expected to be used for electronic materials such as low-dielectric-constant dielectric films as follows.
In the fabrication of semiconductor integrated circuits, as their integration degree becomes higher, an increase in interconnect delay time due to an increase in interconnect capacitance, which is a parasitic capacitance between metal interconnects, prevents their performance enhancement. The interconnect delay time is so-called an RC delay which is in proportion to the product of electric resistance of metal interconnects and the static capacitance between interconnects. Reduction in the resistance of metal interconnects or reduction in the capacitance between interconnects is necessary for reducing this interconnect delay time.
The reduction in the resistance of an interconnect metal or the interconnect capacitance can prevent even a highly integrated semiconductor device from causing an interconnect delay, which enables miniaturization and high speed operation of it and moreover, minimization of the power consumption.
One of the possible methods for reducing an interconnect capacitance is to reduce a dielectric constant of an interlayer dielectric film formed between metal interconnects. A material having a dielectric constant of 2.5 or less is usually prepared by introducing pores inside of the material to make it porous. When an dielectric film is made porous, however, the film has reduced mechanical strength and reliability of it during fabrication of semiconductor devices cannot be ensured. Many investigations have therefore been made in order to improve the mechanical strength of such a porous film. An attempt to use zeolite having pores in the crystal structure of silicon oxide has attracted attentions because it has strength increased by crystallization and is substantially free of a silanol residue and is therefore hydrophobic. There are many reports on it (for example, Adv. Mater. 13, No. 10, 746(2001) or Japanese Patent Provisional Publication No. 2004-165402 by the present inventors).
In use of a thin film for semiconductor devices, what is important is that the film must be free of metal contamination and is homogeneous. In addition, zeolite used for it is required to have a uniform particle size to some extent. As zeolite crystals to be used therefor, those obtained by hydrothermal synthesis in the presence of a structure directing agent are usually employed. As a material to be used in a minute structure of semiconductor devices, the zeolite crystals available by hydrothermal synthesis are not always satisfactory in the particle size and uniformity of it. In particular, a material used in a semiconductor minute structure is required to have a small and uniform particle size because a thin film must be formed from it. It is very difficult to obtain zeolite fine particles having a particle size of 100 nm or less and at the same time, having a uniform particle size.
As an attempt to obtain such a material, Japanese Patent Provisional Publication No. 2004-79592 proposes a process of obtaining zeolite crystals by hydrothermal synthesis, centrifuging and separating them by particle size, removing zeolite crystals and aggregates which have become excessively large, and using only fine crystals having a small particle size.